Hot-gas engines

ABSTRACT

A double-acting hot gas engine includes four or a higher even number of cylinders which comprise pairs whereof the cylinders are phase-displaced through a 180* crank angle. An expansion chamber of each cylinder is connected, by way of a heater, a regenerator and a cooler arranged in series, to a compression chamber of another cylinder. At least for partial load, the compression chambers of each pair are interconnected via an overflow path for a time period extending throughout part of each of successive working cycles of each pair, the time period being increased if the load decreases.

Safies atet 1191 Hubschmann June 4, 1974 HOT-GAS ENGINES 2,611,2359/1952 Van Weenen 60/24 2,643,507 6/1953 Dros 60/24 [75] Inventor: i Pig fiuhglschmann 2,664,699 1/1954 Kohler 60/24 angwe1 erman [73]Assignee: Motoren-Werke Mannheim AG Primary ExaminerEdgar W. GeogheganV0rm- Benz abta o 'fl Assistant ExaminerH. Burks glotmenball, POStfaCh,Mannheim, Attorney, Agent, or Firm-Eric H. Waters ermany [22] Filed:NOV. 14, 1972 [57] ABSTRACT [2]] Appl- NO: 306558 A double-acting hotgas engine includes four or a higher even number of cylinders whichcomprise pairs 30 Foreign Application priority Data whereof thecylinders are phase-displaced through a 180 crank angle. An expanslonchamber of each cyl- Nov. 16, l97l Germany 2156773 mder 15 connected, byway of a heater, a regenerator and a cooler arranged in series, to acompression (gl. chamber of another cylinden At least for partial load58 Field 615651611IIIIIIIIIIIIIIIIIIIIIIIIIIIIII'6o/24, 525 P ChambersOf each. pair imam nected via an overflow path for a time period extend1561 ilsstarzsi rgar ihf2:2 322225 551; 1122213611 UNITED STATES PATENTSthe load decreases 2.480.525 8/l949 Van Weenen 60/24 2,486,081 10/1949Van Weenen 60/24 8 Claims, 4 Drawing Figures PATENTEBJUH 4 IBM f 3313-1sum 1 0F 3 j V 5 A. 10

HOT-GAS ENGINES BACKGROUND OF THE INVENTION l. Field of the InventionThe invention relates to a method of obtaining loadresponsive regulationof the power of a double-acting hot-gas engine comprising four or ahigher even number of cylinders, in which each cylinder contains anexpansion chamber and a compression chamber separated by a workingpiston. For the purpose of achieving the Stirling cycle, each expansionchamber is connected to a compression chamber of another, phasedisplacedcylinder by way of a flowpath which contains a heater, a regenerator anda cooler arranged in series.

2. Description of the Prior Art A hot-gas engine of the above kind isillustrated in FIG. a on page 287 of Motortechnische Zeitschrift, No. 7,Vol. 29 I968) and is briefly described in the associated text. On pages290 and 291 of the same issue of this journal there are given sevenvariables, changes in which enable the power of a hot-gas engine to beregulated, but no details are given as to how such regulation can beachieved in a double-acting hot-gas engine. One of these variables isthe ratio of maximum pressure to minimum pressure in the Stirling cycle.

SUMMARY OF THE INVENTION An object of the present invention is toprovide a method of regulation which results in a change of theaforementioned ratio.

According to one aspect of the invention, there is provided a method ofobtaining load-responsive regulation of the power of a double-actinghot-gas engine which comprises four or a higher even number of cylinderseach of which contains an expansion chamber and a compression chamberseparated by a working piston and which comprise pairs of cylinderswhereof the cylinders of each pair are phase-displaced with respect toeach other through a 180 crank angle, the expansion chamber of eachcylinder being connected, by way of a flow path containing a heater, aregenerator and a cooler arranged in series with one another, to thecompression chamber of another cylinder which is phasedisplaced withrespect to the first-mentioned cylinder through a crank angle which is afraction 180 and the compression chambers of each said pair beingintermittently interconnectable by way of an overflow path, comprising,at least for partial load, interconnecting the compression chambers ofeach said pair by way of the relevant overflow path for a time periodextending throughout part of each of successiv working cycles of eachsaid pair, and increasing said time period if the load decreases.

According to another aspect of the invention, there is provided in adouble-acting hot-gas engine, a combination comprising four or a highereven number of cylinders each of which contains an expansion chamber anda compression chamber separated by a working piston and which comprisepairs of cylinders whereof the cylinders of each pair arephase-displaced with respect to each other through a 180 crank angle, aflow path connecting the expansion chamber of each cylinder to thecompression chamber of another cylinder which is phase-displaced withrespect to the firstmentioned cylinder, each flow path comprising aheater, a regenerator and a cooler arranged in series with one another,an overflow path whereby the compression chambers of each said pair areinterconnectable intermittently, and valve means in each overflow patharranged to open and close the overflow path at intervals.

An overflow of working medium thus occurs during each working cycle atleast in the range of reduced power. The indicator diagram area, andthus the ratio of the maximum pressure to the minimum pressure in thecompression chamber and therefore in the associated expansion chamber,is thereby reduced. The change in the area of the diagram may becompleted in one working cycle, provided that each overflow path is of across-section which permits a virtually unrestricted overflow of workingmedium between the two compression chambers. Assuming that this is so,the regulation takes place with the same low degree of inertia as in aDiesel engine. A further advantage of this invention resides in the factthat neither additional regulating vessels nor an auxiliary compressorare required for the working medium. When the overflow paths areunrestricted regulation occurs in a virtually loss-free manner.

The full capacity of a hot-gas engine of a given size is fully utilizedin an advantageous manner by closing the overflow paths for full load.

' A gradual change from full load to partial load is advantageouslyachieved if the time periods for which the overflow paths are open occurin regions of the working cycles wherein the pressures in the relevanttwo compression chambers are substantially equal to each other at fullloadConsequently, the relatively short open periods associated with highpartial loads occur at zones in the piston travel in which the pressuresin the two compression chambers differ only slightly from each other, sothat only a relatively slight reduction in the diagram area occurs athigh pressure differentials. With increasing open periods, associatedwith lower pressure differentials, a more pronounced reduction in thediagram area of necessity occurs since the open periods extend intozones of piston travel in which the pressures in the two compressionchambers differto an increased extent at full load.

Continuous fluctuations in the diagram area when the load is constantare advantageously avoided by so selecting the positions of the openingand closing points of an open period that occurs or is altered for thefirst time that the opening and closing points of an equally long periodfollowing a crank angle coincide at least approximately with the pointsat which the pressures in the two compression chambers are at the samelevel.

An increase in the dead space in the hot-gas engine is advantageouslyavoided by making the valve means in each overflow path as two shut-offvalves disposed one behind the other in the path.

BRIEF DESCRIPTION OF THE DRAWINGS In order that the invention may beclearly understood and readily carried into effect, reference will nowbe made, by way of example, to the accompanying drawings, in which:

FIG. 1 is a diagrammatic illustration of four cylinders of asix-cylinder hot-gas engine,

FIG. 2 is a diagram showing qualitatively the relationship between thepressures (P) in two interconnectible compression chambers of the engineand the crank DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. I shows onlyfour cylinders I, 2, 3 and 4 of a double-acting six-cylinder hot-gasengine. Each cylinder contains a compression chamber and an expansionchamber 6 separated from each other by a working piston 7. For thepurpose of achieving the Stirling cycle the expansion chamber 6 of eachcylinder is connected to a compression chamber 5 of another cylinderwhich when operating is phase-displaced with respect to thefirst-mentioned cylinder through a 60 crank angle, the connections beingby way of a flow path which contains a heater 8, a regenerator 9 and acooler It) arranged in series with one another. Thus there isconnections between the expansion chamber 6 and the compression chamber5 in the case of each cylinder pair I-2, 2-3, 3-4, 4-5 and 6'-l, thecylinders 5 and 6' not being shown in the drawings. The compressionchambers 5 of each pair of cylinders of which the cylinders, whenoperating, are phase-displaced with respect to each other through a 180crank angle, are interconnectible through overflow paths, only one ofthese paths, designated by the numeral II and between the cylinder I andthe cylinder 4, being illustrated. The overflow path II can beintermittently closed by shut-off members I2 which are operated insynchronism with the associated pistons '7. Apart from the path II, theengine contains two further overflow paths, not illustrated, which canbe intermittently closed in a corresponding manner and which establishconnections between the compression chambers 5 of the cylinder pairs 2-5and 3-6. The cylinders I, 2, 3 and 4 illustrated, as well as thecylinders 5' and 6 which are not illustrated, are filled with a suitablepressurised medium, usually helium. When the operating medium is forcedfrom one of the expansion chambers 6 into the communicating compressionchamber 5 by the phase-displaced movement of the two associated pistons7, it stores most of its heat picked up from the heater 8 in theregenerator 9, whereas a smaller portion of the heat is yielded tocooling water'in the cooler I0. Thus, heat is extracted from theoperating medium in this process and for this reason the compressionchambers S are also called cold chambers. The heaters 8 are heated in amanner not illustrated by an external source of heat, e.g., an oilburner. When the operating medium is forced from one of the compressionchambers 5 into the communicating expansion chamber 6 by thephase-displaced movement of the two associated pistons 7, it firstabsorbs the heat stored in the regenerator 9 and then is further heatedin the heater 8. Thus, heat is supplied to the operating medium in thisprocess and for this reason the expansion chambers 6 are also called hotchambers. The phase displacement between the movements of the individualpistons 7 has the effect of intermittently reducing and increasing thechambers 5 and 6 interconnected in each case through the elements 8, 9and 10,

the compression of the operating medium taking place in the coldcondition and its expansion in the hot condition. In this way an outputof mechanical work is achieved, and this output is represented in thediagram of FIG. 4 by the area enclosed by the solid line, which relatesto the full-load condition. In FIG. 4 the upper portion of the linerepresents the expansion process and the lower portion the compressionprocess. In FIG.

2 the change in pressure in the chamber 5 of the cylinder I in relationto the crank angle (15 is shown by the curve I and that in chamber 5 ofthe cylinder 4 by the curve IV, both for the full-load condition. FIG. 3shows what is meant by the crank angle (1). Under full load the shut-offmembers 12 are closed. Thus there is no overflow between the chambers 5of any of the cylinders in this condition. Under partial load theshut-off members I2 are opened in the regions of the points A (FIG. 2)in the piston travel during each working cycle. When the shut-offmembers I2 open for the first time at points I and 4 on the curves I andIV, equalization of pressure occurs as indicated by the lines M and 4-4.The resultant confluence pressure does not necessarily occur aboutmidway between the pressures at points I and 4 as shown in FIGS. 2and'4, but depends upon the ratio of the energy contents of theoperating medium in the interconnected chambers 5. The shut-off membersremain open as far as the points designated I and 4" on the curves I andIV, so that a change in pressure corresponding to the curves I and IVnow occurs. As can be seen from the broken-line curves in FIG. 4, thetotal diagram area is smaller than at full load, i.e., the powerprovided by the hot-gas engine is adapted to suit a reduced load. As thepartial load increases, the points I, 4 and 4", 4 move progressivelynearer to the points A until, at full load, they coincide with them.

I claim:

I. A method of obtaining load-responsive regulation of the power of adouble-acting hot-gas engine comprising an even number of cylinders ofat least four, each cylinder containing an expansion chamber and acompression chamber separated by a working piston, grouping saidcylinders in pairs of cylinders, phasedisplacing the cylinders of eachpair with respect to each other through a crank angle, connecting theexpansion chamber of each cylinder, by way of a flow path containing aheater, a regenerator and a cooler arranged in series with one another,to the compression chamber of another cylinder which is phase-displacedwith respect to the first-mentioned cylinder through a crank angle whichis a fraction of 180, the compression chambers of each pair beingintermittently interconnectable by way of an overflow path, at least forpartial load, interconnecting the compression chambers of each pair ofcylinders by way of the respective overflow path for a time periodextending throughout part of each of successive working cycles of eachpair, and increasing said time period if the load decreases.

2. A method according to claim I, and the step of maintaining theoverflow paths closed at full load.

3. A method according to claim I, wherein the time periods for which theoverflow path of each pair of cylinders is open occur in regions of saidworking cycles wherein the pressures in the respective two compressionchambers would be substantially equal to each other at full load.

4. A method according to claim 3, wherein said time periods for whichthe overflow path of each pair is open, are displaced through 180 crankangle with respect to one another.

5. In a double-acting hot-gas engine, a combination comprising an evennumber of cylinders of at least four, each cylinder containing anexpansion chamber and a compression chamber separated by a workingpiston, said cylinders being grouped in pairs of cylinders, thecylinders of each pair being phase-displaced with respect to each otherthrough a 180 crank angle, a flow path connecting the expansion chamberof each cylinder to the compression chamber of another cylinder which isphase-displaced with respect to the firstmentioned cylinder through acrank angle which is a fraction of 180, each flow path comprising aheater, a regenerator and a cooler arranged in series, an overflow pathfor interconnecting intermittently the compression chambers of eachpair, and valve means in each overflow path for opening and closing theoverflow path at intervals.

6. A combination according to claim 5, wherein said valve means in eachoverflow path comprises first and second valve means adjacent therespective compression chambers interconnectable via said overflow path.

working piston.

1. A method of obtaining load-responsive regulation of the power of adouble-acting hot-gas engine comprising an even number of cylinders ofat least four, each cylinder containing an expansion chamber and acompression chamber separated by a working piston, grouping saidcylinders in pairs of cylinders, phase-displacing the cylinders of eachpair with respect to each other through a 180* crank angle, connectingthe expansion chamber of each cylinder, by way of a flow path containinga heater, a regenerator and a cooler arranged in series with oneanother, to the compression chamber of another cylinder which isphasedisplaced with respect to the first-mentioned cylinder through acrank angle which is a fraction of 180*, the compression chambers ofeach pair being intermittently interconnectable by way of an overflowpath, at least for partial load, interconnecting the compressionchambers of each pair of cylinders by way of the respective overflowpath for a time period extending throughout part of each of successiveworking cycles of each pair, and increasing said time period if the loaddecreases.
 2. A method according to claim 1, and the step of maintainingthe overflow paths closed at full load.
 3. A method according to claim1, wherein the time periods for which the overflow path of each pair ofcylinders is open occur in regions of said working cycles wherein thepressures in the respective two compression chambers would besubstantially equal to each other at full load.
 4. A method according toclaim 3, wherein said time periods for which the overflow path of eachpair is open, are displaced through 180* crank angle with respect to oneanother.
 5. In a double-acting hot-gas engine, a combination comprisingan even number of cylinders of at least four, each cylinder containingan expansion chamber and a compression chamber separated by a workingpiston, said cylinders being grouped in pairs of cylinders, thecylinders of each pair being phase-displaced with respect to each otherthrough a 180* crank angle, a flow path connecting the expansion chamberof each cylinder to the compression chamber of another cylinder which isphase-displaced with respect to the first-mentioned cylinder through acrank angle which is a fraction of 180*, each flow path comprising aheater, a regenerator and a cooler arranged in series, an overflow pathfor interconnecting intermittently the compression chambers of eachpair, and valve means in each overflow path for opening and closing theoverflow path at intervals.
 6. A combination according to claim 5,wherein said valve means in each overflow path comprises first andsecond valve means adjacent the respective compression chambersinterconnectable via said overflow path.
 7. A combinatiOn according toclaim 5, wherein said valve means in each overflow path comprises afirst control aperture formed in a member connected to the workingpiston of a cylinder of the respective pair, and a second controlaperture formed in a regulating sleeve and co-operating with said firstcontrol aperture.
 8. A combination according to claim 7, wherein eachsaid member is a piston rod co-axial with the respective working piston.